1. Field of the Invention
The present invention is directed to devices and methods for improving the integrity and performance capabilities of guardrail installations. In particular, the invention is directed to devices and methods for strengthening the support posts and entire installation to accommodate redirection impacts along the length of a guardrail.
2. Description of the Related Art
Guardrail installations are longitudinal safety devices that extend along the sides of highways and roadways. In their usual construction, a corrugated rail member is supported above the ground by a number of support posts that are often fashioned of wood. The rail member is interconnected to each post by a connection bolt that passes through a drilled hole in the post.
Guardrail installations usually experience two types of vehicle impacts, and should be designed to function well in response to each. The first type of impact is an end-on impact in which one end of the guardrail installation is impacted by a vehicle that approaches the guardrail from a substantially end-on direction. In this type of impact, the guardrail installation should perform in a controlled manner in order to absorb the energy of the colliding vehicle. To accommodate this performance, frangible (or break-away) posts, which are structurally weakened at or near the ground level to assist in breaking the post away, are sometimes used at the upstream end of a guardrail installation. A number of guardrail end treatments have been devised to assist the controlled performance of the rail member during an end-on impact. These include the guardrail extruder terminal, which is known commercially as the ET-2000, and the slotted rail terminal.
The second type of impact that a guardrail should be designed for is a redirection impact wherein a colliding vehicle approaches and engages the guardrail substantially from the lateral side. In this type of impact, the role of the guardrail installation is to redirect the vehicle back into its lane of traffic and provide a resilient, but non-yielding barrier that will prevent the colliding vehicle from penetrating the rail member and passing through to the opposite side of the guardrail installation. This aspect of guardrail design is important because a colliding vehicle that passes through a guardrail might travel into an area of extreme danger, such as a lane of traffic moving in the opposite direction or toward a precipice. This barrier role is the principal function of a guardrail installation.
The inventors have determined that the point at which the connection bolt passes through the guardrail post is a location of true vulnerability for the support posts during a redirection impact. The presence of the drilled hole for the guardrail attachment bolt has weakened the post to a degree. In addition, forces applied to the bolt from the rail member, as might occur in a redirection impact collision, impart strong forces to the drilled hole which can easily split the post in half. When this occurs, the posts may split and, thus, the rail member may be released from the posts, and the ability of the guardrail to prevent a colliding vehicle from passing through it is compromised or destroyed. The inventors have learned through crash testing that such failures often cause the guardrail to lose integrity and allow vehicles to penetrate the guardrail.
In the past, attempts to strengthen guardrail installations against penetration from redirection impacts have focused on increasing the number of support posts that anchor the rail member to the ground or by using larger, thicker support posts, or both. Unfortunately, these options significantly increase the expense of the guardrail installation. More importantly, however, they inhibit the ability of the guardrail to perform its other intended purpose providing a controlled activation or collapse during end-on impacts. Larger and stronger posts, or an increased number of posts, stiffen the guardrail system and degrade its ability to perform in an acceptable manner during an end-on impact. In addition, an impact by a vehicle with a thicker, stronger post may stop the vehicle abruptly and severely damage it, resulting in greater injuries to the occupants.
It would be an improvement to have a device and method that addresses the problems of the prior art.
The present invention provides devices and methods for strengthening the upper portions of the support post assemblies of guardrails and guardrail end treatments against the forces that are imparted to the post during an impact. The upper portions of support posts, particularly the areas proximate the bolt connection, are reinforced. Preferably, a compressive force is applied to those areas as well by the reinforcements.
In one preferred embodiment, reinforcement for the upper portion of the post is provided by metal banding that is disposed around the periphery of the post. Alternative exemplary embodiments are also described in which reinforcement to the upper portion of the post is provided by plates that are secured into place at a location proximate the connection bolt or by a metal cap that sits atop the post. In a further alternative embodiment, a strengthened support post assembly is provided by eliminating from the post the drilled hole and connection bolt disposed therewithin. The rail member is instead affixed to a collar that surrounds the post.
The methods and devices of the present invention optimize the strength of the support post assemblies for guardrail installations. They also allow guardrail installations to be inexpensively strengthened to provide increased redirection capability in response to redirection impacts. At the same time, the guardrail installation""s ability to collapse in a controlled manner in response to end-on impacts is not reduced.